private byte ShiftRightMsb(byte value)
{
var lo = value.AND(1);
var hi = value.AND(128);
var r = value.RS().OR(hi); // Keep MSB
FC = lo == 1;
FH = false;
FN = false;
FZ = r == 0;
return(r);
}
private byte Swap(byte value)
{
var hi = value.AND(_u4).LS(4);
var lo = value.AND(240).RS(4);
var r = hi.OR(lo);
FC = false;
FH = false;
FN = false;
FZ = r == 0;
return(r);
}
public override void Write(ushort address, byte value)
{
if (address <= 0x1FFF)
{
_enabled = value.AND(0x0A) == 0x0A;
}
else if (address >= 0x6000 && address <= 0x7FFF)
{
_ramEnabled = value == 0;
}
else if (_ramEnabled && address >= 0x4000 && address <= 0x5FFF)
{
_ramBankIndex = value.AND(0x03);
}
else
{
base.Read(address);
}
}
private byte ShiftLeft(byte value)
{
var hi = value.AND(128).RS(7);
var r = value.LS();
FC = hi == 1;
FH = false;
FN = false;
FZ = r == 0;
return(r);
}
private byte ShiftRight(byte value)
{
var lo = value.AND(1);
var r = value.RS(); // Zero out MSB
FC = lo == 1;
FH = false;
FN = false;
FZ = r == 0;
return(r);
}
private byte RotateLeft(byte value, bool resetZ = false)
{
var hi = value.AND(128).RS(7);
var r = value.LS().OR(FC);
FC = hi == 1;
FH = false;
FN = false;
FZ = resetZ ? false : r == 0;
return(r);
}
private byte RotateRight(byte value, bool resetZ = false)
{
var lo = value.AND(1);
var r = value.RS().OR(FC.LS(7));
FC = lo == 1;
FH = false;
FN = false;
FZ = resetZ ? false : r == 0;
return(r);
}
public override void Write(ushort address, byte value)
{
if (address >= 0x2000 && address <= 0x3FFF)
{
byte lowerFiveBits = value.AND(0x1F);
_romBankIndex = _romBankIndex.AND(0xE0).OR(lowerFiveBits);
}
else if (address >= 0x4000 && address <= 0x5FFF)
{
byte upperTwoBits = value.AND(0x03);
_romBankIndex = _romBankIndex.AND(0x1F).OR(upperTwoBits.LS(5));
}
// Invalid bank indexes jump to the next index
if (_romBankIndex == 0x00 ||
_romBankIndex == 0x20 ||
_romBankIndex == 0x40 ||
_romBankIndex == 0x60)
{
_romBankIndex++;
}
}
private byte RotateLeftC(byte value, bool resetFz = false)
{
var hi = value.AND(128).RS(7);
var r = value.LS().OR(hi);
FC = hi == 1;
FH = false;
FN = false;
// Some instructions unconditionally reset FZ even if the result is 0
// This differs from the official docs, but several ref impl's confirm this behavior
FZ = resetFz ? false : r == 0;
return(r);
}
private void GetBit(byte value, byte bitMask)
{
FH = true;
FN = false;
FZ = value.AND(bitMask) == 0;
}
